1. Field of the Invention
The present invention relates generally to the fields of immunology and monoclonal antibody production. More particularly, the present invention concerns anti-IgM monoclonal antibodies and methods for their use.
2. Description of the Related Art
Since the initial description of monoclonal antibodies, the development of technology to produce immortalized lymphocytes capable of producing antibodies of predetermined specificity has had a major impact on both clinical and basic scientific research as well as the therapeutic modalities available for the diagnosis and treatment of a wide variety of pathological conditions.
Antibodies are endogenous proteins produced by the immune system in response to antigenic stimuli. These proteins specifically bind to antigen molecules at defined sites (epitopes). Polyclonal antibodies are derived from immunization of animals with antigens and bind to these antigens at multiple epitopes. Monoclonal antibodies, on the other hand, are a specific, defined set of antibodies which are derived from a single clone (monoclone) of cells producing a specific antibody. In contrast to polyclonal antibodies monoclonal antibodies bind to only one specific epitope on the antigen molecule.
Although the technology for the generation of monoclonal antibodies has existed for some time, the current methodology is time-consuming, laborious and often results in the production of antibodies which, although specific for the target antigen, are of relatively low affinity for the antigen, and thus are of limited usefulness in a wide variety of applications.
Among the difficulties encountered in the production of useful and clinically relevant monoclonal antibodies is the abundance of antibodies of the IgM sub-type obtained from hybridomas produced by standard in vivo or in vitro immunization procedures. The IgM sub-type antibodies are generally of low affinity, are difficult to purify and often comprise the bulk of antibodies produced by hybridomas. In addition, in mixed cultures of IgM and IgG secreting hybridoma cells, IgM secreting cells often overgrow the IgG secreting hybrid cells.
Part of the laborious procedure for the production of hybridomas is the elimination of the IgM producing hybridoma cells produced after a cell fusion. This is generally done by cloning the cells by limiting dilution, growing up the individual cells into colonies, and testing each colony individually to determine which colonies produce IgG sub-type antibodies. Generally, the IgG producing hybridoma cells are then further analyzed to determine the antigen specificity of the antibodies produced.
Although antibodies have been reported which are directed against epitopes on the IgM antibody, all tested to date were also reactive with IgG sub-type antibodies.
Linking cytotoxic agents to antibodies to make "immunotoxins" has been disclosed by the applicants and others. Recent interest has centered on immunotoxins of monoclonal antibodies conjugated to the enzymatically active portions (A chains) of toxins of bacterial or plant origin via hetero-bifunctional agents. Nevelle, D. M. and Youle, R. J., Immunol Rev (1982) 62: 75-91; Ross, W. C. J., et al., European J Biochem (1980) 104; Vitteta, E. S., et al., Immunol Rev (1982) 62: 158-183; Raso, V., et al., Cancer Res (1982) 42: 457-464; Trowbridge, I. W. and Domingo, D. L., Nature (Lond) (1981) 294: 171-173.